Transformer apparatus



May 3, 1966 l.. A.|1E5LAR 3,249,851

TRANSFORMER APPARATUS Original Filed March 15. 1957 3 Sheets-Sheet 1 I N VE N TOR fw/cs A7. f-oma',

BYMQ/u ATTORNEY5 May 3, 1966 L. A. MEDLAR 3,249,851

TRANSFORMER APPARATUS I Original Filed March l5, 1957 5 Sheets-Sheet 2 I N VE N TOR EW/s xv: Mraz/71.

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ATTORNEYS May 3, 1966 L.. A. MEDLAR 3,249,851

TRANSFORMER APPARATUS Original' Filed March 15, 1957 3 Sheets-Sheet 3 lll 1N VENTOR EW/5 I. Eme

United States Patent O 3,249,851 TRANSFORMER APPARATUS Lewis A. Medlar, Lansdale, Pa., assignor to Fox Products Company, Philadelphia, Pa., a corporation of Pennsylvama Original application Mar. 15, 1957, Ser. No. 646,429, now

Patent No. 2,999,973, dated Sept. 12, 1961. and this application Aug. 21, 1961, Ser. No. 132,845

12 Claims. (Cl. 323-60) This invention relates to a transformer system for supplying power from an A.C. input to aA load, and, more particularly, to a transformer system for supplying a substantially constant current toa load subject to variations of impedance. This application is a division of my copending application Serial Number 646,- 429, filed March 15, 1957, and now U.S. Patent 2,999,- 973.

As will be understood after the following explanation, the transformer system of this invention is capable of supplying a large number of different characteristic outputs. Among such'outputs are a characteristic rise of current output with increasing load, a characteristic drop of current output with increasing load, and a substantially constant current output with increasing load. The invention will be more fully described in conjunction with the last-mentioned characteristic, which is preferred, but it will be understood that the invention is not limited to this characteristic.

In the past, several different means of obtaining a substantially constant current output with changing load impedance have been evolved. Perhaps the earliest of these various systems is that using a movable coil, the coil being counter-balanced and automatically adjusted in accordance with changing load to vary the distance between the input and output sides of the transformer and thereby to vary the coupling. This system is still in use today for constant current lighting systems, but it is subject to several disadvantages, among which are poor speed of response, the substantial expense of the system, the bulkiness of the unit, and the use of moving parts subject to wear and eventual shutdown of the system.

Another past-suggested constant current apparatus uses a saturable core reactor. The reactor may be a relatively simple one or may be a complex system utilizing shunts, partial air gaps, etc. This type of system, however, is relatively expensive, as well as being complex. Moreover, it has a lagging power factor. y

A third general type of known constant current system is one using a resonance phenomenon. This type of system has -taken many forms, but the simplest form is the series resonant circuit, including an inductive reactance and a capacitive reactance connected in series, the two reactances being .adjusted to be substantially equal, and the load being connected across one of the reactances. While this type of system provides quite good constancy of output current, it has been found necessary to provide auxiliary means to limit the voltages across the components on open circuit. Moreover, this type of system is not readily l'adjustable to change the level of output current which is to be maintained constant. Inorder to provide for such change, there must be a change in both the actual inductance and the actual capacity vlof the components.

Another adaptation of the resonant system is the socalled monocyclic square. This system is subject to several of the disadvantages enumerated above for the simple series resonant system.

In contrast to all of the above previously suggested systems, the transformer system of the present invention provides a substantially constant current output at Divided change the level of output current to be maintained constant, and for a substantially lower cost than many of the previous systems.

The transformer system of this invention is in the nature of a resonant phenomenon, but, as will be obvious from the theoretical analysis to follow, it is far from a'simple resonant phenomenon. None of the various embodiments of the invention to be described uses a simple series resonant circuit, and all of the embodiments actually automatically adjust themselves to maintain a substantially resonant condition even with change of only one of the components, such as change in capacity. The system is not dependent for its operation upon leakage reactance or on saturation of the core or any of its components, and the system actually is limitedv and adversely affected in its operation by these ever-present effects.V

One important advantage of the transformer system of this invention is the fact that it draws a leading power factor current from the input, rather than the lagging power factor usually obtained with a transformer system.

The apparatus of the present invention is capable of use wherever it is desired to draw a substantially constant current through a variable load, when a constant voltage input is provi-ded. One instance of such use is in lighting systems.

The apparatus of the present invention, generally described, includes an input, an output, and a control electrical circuit, each of these circuits including at least one coil which may be wound on a transformer core. The coils of the input and output electrical circuits are so inductively related, wound and connectedV with respect to one another that two magnetic circuits, an input and an output, are formed. The magnetic circuits have two common portions, inone of which the magnetomotive forces generated by the input and output currents aid, an-d in the other of which the magnetomotive forces generated by these currents oppose. As a result, there is no direct coupling of power between the input circuit andthe output circuit. The control electrical circuit includes a capacitor and as inductively erates a magnetomotive force which is opposite in phase and of greater magnitude than the output magnetomotive `force in the common portion through which the y coupling takes place. The control magnetomotive force in elect reverses the output magnetomotive force in said common portion of the magnetic circuit and hence couples power from the input to the output through the control electrical circuit. l

`The invention will now be described in conjunction with the accompanying drawings, showing preferred embodiments thereof.

In'the drawings: FIG. l is a schematic diagram of a transformer system in accordance with the invention;

FIG. 2 is ian equivalent electrical circuit diagram for the system of FIG. 1;

FIG. 3 is a diagrammatic illustration of the magnetic vcircuits of the transformer system of thisl invention;

FIG. 4 is a schematic diagram of a transformer apparatus similar to that of FIG. l but with load connected across the terminals which are the input terminals in FIG. l andv the input connected across the terminals which are the load terminals in FIG. 1;

3 4f FIG. 5 is a schematic diagram of a transformer ap control coil current is shown as IL, the output current paratus in accordance with the invention illustrating the is shown as Ie, land the output or load impedance is Z, use of a control coil in the control electrical circuit and In this circuit the mutual inductance, or inductive coupling, the various connections ipossible with this control coil; ,between coils L1 and L2 is shown as Mn between coils FI.G' Slis Shematic etiaglrartl showtingl a, del/tice for 5 L1 and L3 is M2, and between coils L2 and L3 is M3.

7 aelicilatamtsilwlgclformer Using 11:1@ Setting PP 1.116811 equations for the input Coupling of the capacitor in the control circuit; and output and control circuits, assuming .one:one turns FIG. 8 is a schernatic diagrarn illustrating the use et ratios, neglecting ohmic resistance of coils, leakage re a saturable transformer to vary the effective capacity of in actarlce and Coro loss, and Soll/lng for the load current, the capacitor in the control circuit. we obtain the following equation:

Referring now to the drawings in detail, it will be It is evident that the above equation is relatively comseen that all of the embodiments of the invention illusplicated and not susceptible of easy analysis, -but it will trated include a four-legged shell-type core 50 carrying be noted that the impedance value Z appears in only one Litt-Mi2 im at least three coils, two of the coils being connected in term, that being in the denominator of the equation. For series, with the load connected lacross one of the third the load current Io to be entirely independent of load, the coil and the series 4combination of the rst two coils, multiplier of the impedance Z must be zero, so We oband the input being connected across the other of the tain: third coil and the series combination of the first and' L second coils. A capacitor is connected in a control circuit ptK -l-L 1 =0 inductively coupled to one of the rst and second coils. ILS-M32 The core may be formed ofany appropriate material, This Obviously iS the Condition for Por@ constancy of but it will lbe preferable in most cases that a standard the load, 01 Output, curfe1t- Through Simple arithmetical transformer iron core -be used and that stampings be operations 011 the last equatiohwo obtaih assembled together to form the usual transformer lamina 2 L1L3 M 3 1 tions. With such a structure, magnetic paths are formed w L1 wK between the two outer legs yof the core and between the outer legs and the center legs. If a ferromagnetic 35 Tins iasiequation is obviously for a resonant System' core material is employed, as is preferred, the permeability but it also is obviously not a Simple resonance equation' df the ,paths Will he highin comparison With air* The transformer .coils and connections of FIG. l form In the basic system of this invention, as shown in FIG. two magnetic c iieuits in the transformer core' The nist 1, coil L1 is wound around inner legs 51 and 52 of the inagnetie Circuit as shown in FIG; @includes portions transformer, with each turn of the coil encircling both ,tu ib--hg-l ano 7-cde*fig This circuit is that tol' of ,the legs Coil L2 is Wound cn leg 51, .and coil L3 lowed by ilux driven by the primary magnetomotive force, is Wound aule'g 52 as shown in FIG. 3, with Fr representing the primary The input source of A.-C. voltage of constant magnitude The Second magnetitc circuit includes the Por' 53 is connected across coil L1, while a load 54 is contions bc-"gi of the core material- This magneticv nected across the series combination of coils L2 and L3. eiienit is traversed by n nX driven iy the ontpnt magneto A capacitor K is connected directly across coil L3. motive torce Fo- It Will be Seen that in Portion b-g 0f The transformer core, in addition to inner legs 51 the left inner iegfne input and output magnetomotive and 52, alsol has outer legs 55 and 56, no coil being Wound forces oppose While in portion c-f of 'the right inner on either of these legs. Outer leg 55 includes portion ieg the ontpnt and 1nput magnetomotive forces aidb a h g cf thc core, inner leg 51 includes portion If no control circuit were employed, there would hence be t. b g f, inner leg 52 pdrtien d c f e, and outer leg 50 no coupling of power ybetween the input and the load be- 56 portion ne The POrtiens h, b g u f, and d e et cause the voltages in the differentially wound coils would the teur legs are substantially parallel te each ethen cancel each other. However, the control coil current It is not necessary that the legs of the core be coplanar, generates a magnetomotive force FI- Wnieh is opposed to or parallel, as shown in the drawings, or that the core the magnetomotive torce F0 in Portion cof the right he tree et air gans. It is 0nly necessary that magnetic 55 inner leg, and is of such a higher magnitude, that the repaths he formed ,between all legs et the cere As a matter sultant .between the control and output magnetomotive er fact, =as indicated above, the cere rnaterial may he forces in this leg is substantially reversed from Ft, and non ferrenlagnetie er air, as .leng as the increased reine reliectsinto the primary or input circuit. Consequently, tance and leakage et such a cere is not tec irnnertant power 1s coupled between the input and the load through or is compensated for by proper selection of the other 60 the control electrical circoitparameters et the system In general, operation of the transformer apparatus These connections provide an iniput electrical circuit above oesoii'ied is Similar to that explained in detail in including coil L1 and its connections connected directly my eopending application Serial Number 646,429, tiled across input 53, an output electrical circuit including coils Maren' 15 i957 of which the present application is a di L2 and L3 and their connections connected directly across 65 Vision and said coperiding application sets out in detail a lead 54, and a |central electrical circuit including coil vector analysis, and characteristic curves, applicable to L3 and capacitor K. Load 54 may be of any type, ,but if the apparatus here iescrineti constancy of current is desired, it is preferred that the In contrast to the simple resonant circuit of the Prior load be mostly resistive in character, land, for best conait the current regulation which cari be obtained With de' stancy, it is preferred that the lead should he suhstantially vices constructed in accordance with the invention is subef unity newer factcn stantially the same for each preselected value of capaci- The equivalent electrical circuit for the apparatus of tance, and the system apparently automatically Changes FIG. 1 is shown in FIG. 2, in which the voltage supplied the mutual inductance between coils on different legs so to goil Lr by the input 53 is Shown as En, the current as to adjust the apparent reluctance of the core and corndriven thereby through the primary is shown as Ip, the pensate for the changed capacity in the control circuit.

-trol coil.

Referring now to FIG. 4, the load 54 can be connected directly across coil L1, and the input 53 be conected across the series combination of coils L2 and L3. This connection of the system results in substantially the same operation obtained with the connections shown in FIG. 1.

Referring to FIG. 5, it is possible to use a separate coil for the control circuit, and such a coil is shown as L., in this ligure. With the separate coil, the control voltage available to drive the capacitor may be increased to a higher level, and the control circuit may obtain its voltage from any appropriate source. For instance, as shown in FIG. 5, the series combination of control coil L4 and the capacitor C may be connected across L1, coil L2, coil L3, the series combination of coils L3 and L3, any other source of voltage, or those terminals may Ibe shorted. Various different characteristics may be obtained through use of these diterent connections, butthe constancy of output current will be good with any of them, being best in that range when the control current is substantially 90 out of phase with the primary voltage at zero load voltage.

The capacitor in the control circuit of FIG. 5 is identified as C, rather than as K in the preceding gures. This indicates use of an actualr capacitor, while the letter K has been used to represent an effective capacity. The equations have also been derived for effective capacity K, but the effect of the control coil can be taken into account in the equations by inserting for K the term 182C, where =l|a, and a is the turns ratio between load coil L3 and control coil L4.

For commercial use, it will be advantageous to provide for adjustment of the level of the output current Vwhich is to be maintained constant with the various embodiments of this invention. Such adjustment may be obtained by varying the capacity of the capacitor, but, especially at voltages of the magnitude used with a transformer system of this type, it will be preferable to vary the effective capacity of the capacitor in the control circuit, rather than the actual capacity. An instance of such variation is shown in FIG. 6, which shows a variable -inductor 60 shunted directly across capacitor K. Variation in the inductance of this inductor causes variation in the effective capacity in the control circuit, so that adjustment in the output current may be obtained.

It is unnecessary that the capacitor of the control circuit be physically present in the connections to the con- As a matter of fact, it will be preferable in many instances to couple the capacitor into the control coil circuit indirectly. FIG. 7 shows such coupling by means of a transformer T, the secondary of the transformer being connected directly across capacitor C, and the primary Vbeing. connected across control coil L3. Moreover, the capacitor might be coupled into the circuit through a variable transformer, or Variac, so providing for adjustment of K by variation in transformer turns ratio.

A system for providing transformer coupling of the capacitor into the control coil circuit, while also providing for variation in the effective capacity in the control circuit, is shown in FIG. 8. This system includes a saturable transformer 61 provided with a secondary coil 62 on its center leg. The secondary coil is connected directly across the capacitor. The two outer legs of the transformer are provided with series-connected coils 63 and 64 to which is connected -a source of variable D.C. voltage 65. The primary coil of transformer 61 is connected directly across control coil L3.

As a result of these connections, variation in the value of voltage supplied to the coils 63 and 64 causes variation in the direct current owing through these coils, and hence of the saturation of the core, thus causing a corresponding change in the primary exciting current and resulting in variation of the effective capacity in the control circuit.

As explained above, all of the embodiments of the invention have a substantially unlimited constancy action 6 with variation in capacity of the control circuit capacitor. When leakage reactance is ignored, all embodiments described have unlimited constancy. This surprising result is achieved by automatic variation in the mutual inductance of coils on separate legs to compensate for changes in capacity, so that resonance is substantially maintained. As far as is known, the action of transformer systems in accordance withthe invention in varying mutual inductance, automatically, without adjustment of parts, is novel.

It will be obvious that many minor variations could be made in the elements` of the various embodiments of this invention shown and described without departure from the spirit of the invention. For instance, the positions of the various coils on the respective legs of the transformer core could be changed about and the characteristics fundamental to the system still be maintained. From the description of the various embodiments, it will be evident that -all of these embodiments have the following in common:

The embodiments include two magnetic circuits, which have two common portions, in one of which common portions the input and output magnetomotive forces aid, and in they other of these two common portions the input and output magnetomotive forcesoppose, so that there is no direct coupling between the input and the load. The control magnetomotive force in effect reverses the total or resultant magnetomotive force in its common portion from the direction of the output MMF, so as to couple power from the input to the load through the control electrical circuit. From the above, it will be obvious that this invention is not to be considered limited to the various embodiments shown and described, but rather only by the scope of the appended claims.

What is claimed is:

1. A transformer system for supplying power to a load from an A.C. input comprising a four-legged core of ferromagnetic material, said legs being of such configuration and so aligned with each other that substantially closed high permeability paths are formed between all of the legs of the core; at least three coils wound on said core, a rst and a second of said coils being wholly wound on a first and a second of said legs, respectively, l.and connected in series, a third of said coils being wound with each turnthereof encircling both of and only said rst and second legs; an input, an output, and a control electrical circuit, all passing current, the input circuit including one of (a) said third coil and (b) the series combination of said first and second coils and being connected across said A.C. input, the output circuit including the other of (a) said third coil and (b) the series combination of said rst and second coils and being connected across said load; said input and output electrical circuits yforming with said core an input and an output magnetic circuit, one including at least substantial portionsL of all four of said legs and the other including said first and second legs, said input and output electrical circuits being so inductively related to said rst and second legs that the input and output magnetomotive forces generated by the input and output currents aid in one of said rst and second legs and oppose in the other of said first and second legs; and a capacitive reactance, said control electrical circuit including said capacitive reactance and being inductively coupled to the leg on which one of said first and second coils is wound; whereby all power coupled between said input and output electrical circuits is immediately coupled through said control electrical circuit, the control current producing a magnetomotive force in said one of said rst and second legs is of phase and magnitude to produce a resultant of said control and output magnetomotive forces opposite to the output magnetomotive force in said last-mentioned leg and thereby to couple power from the input to the load through -said control electrical circuit and said output electrical circuit.

2. The apparatus of claim 1 in which said control electrical circuit includes said rst coil and said capacitive reactance is shunted across said lirst coil.

3. The apparatus of claim 1 in which said input electrical circuit includes said third coil and said output electrical cir-cuit includes the series combination of said first and second coils.

4. The apparatus of claim 1 in which said input electrical circuit includes the series combination of said first and second coils and said output electrical circuit includes said third coil.

5. The apparatus of claim 1 in which said control electrical circuit includes a control coil Wound on the leg on which said one of said first and second coils is Wound.

6. The apparatus of claim 5 in which the series cmbination of said control coil and said capacitive reactance is connected across a source of voltage.

7. The apparatus of claim 6 in which the series combination of said control coil and said capacitive reactance is connected across at least one of said rst, second, and third coils.

8. The apparatus of claim 5 in which the series combination of said control coil and said capacitive reactance is connected across said one of` said rst and second coils.

9. The apparatus of claim 5 in which the capacitive reactance is shunted across the control coil.

10. The apparatus of claim 1 in which said control electrical circuit includes a variable inductive reactance shunted across the capacitive reactance to permit variation of the eiective capacity and hence of the output current.

11. The apparatus of claim 1 in which said control electrical circuit includes a saturable core transformer, at

least one coil wound on the core of said transformer, a source of D.C. voltage connected to said last-mentioned coil and variable to change the saturation of the transformer core, a secondary coil wound on said transformer core and connected across said capacitive reactance, and a primary coil inductively coupled to said secondary coil. 12. The apparatus of claim 1 in which said control electrical circuit includes a transformer having a primary and a second-ary coil, said capacitive reactance being connected across Said secondary coil, and said primary coill beinginductively coupled to said secondary coil.

References Cited by the Examiner UNITED STATES PATENTS 1,599,570 9/ 1926 Lucas 323-60 1,828,900 10/ 1931 Kouyoumjian.

1,830,232 11/1931 Kouyoumjian 323-50 1,860,543 5/1932 Kouyoumjian 323-50 X 2,195,969 4/ 1940 Miner 323-60 X 2,207,234 7/1940 Bohm 323-60 X 2,212,198 8/1940 Sola 323-60 X 2,281,593 5/ 1942 Odessey 323-56 2,305,153 12/1942 Fries 324-60 X 2,403,393 7/ 1946 Peterson 323-60 X 2,512,976 6/ 1950 Smeltzly 323-6 2,605,457 7/ 1952 Peterson 323-6 X 2,811,689 10/1957 Balint 323-60 X LLOYD MCCOLLUM, Primary Examiner.

MILTON O. HIRSHFIELD, Examiner.` W. E. RAY, Assistant Examiner. 

1. A TRANSFORMER SYSTEM FOR SUPPLYING POWER TO A LOAD FROM AN A.C. INPUT COMPRISING A FOUR-LEGGED CORE OF FERROMAGNETIC MATERIAL, SAID LEGS BEING OF SUCH CONFIGURATION AND SO ALIGNED WITH EACH OTHER THAT SUBSTANTIALLY CLOSED HIGH PERMEABILITY PATHS ARE FORMED BETWEEN ALL OF THE LEGS OF THE CORE; AT LEAST THREE COILS WOUND ON SAID CORE, A FIRST AND A SECOND OF SAID LEGS, RESPECTIVELY, WOUND ON A FIRST AND A SECOND OF SAID LEGS, RESPECTIVELY AND CONNECTED IN SERIES, A THIRD OF SAID COILS BEING WOUND WITH EACH TURN THEREOF ENCIRCLING BOTH OF AND ONLY SAID FIRST AND SECOND LEGS; AN INPUT, AN OUTPUT, AND A CONTROL ELECTRICAL CIRCUIT, ALL PASSING CURRENT, THE INPUT CIRCUIT INCLUDING ONE OF (A) SAID THIRD COIL AND (B) THE SERIES COMBINATION OF SAID FIRST AND SECOND COILS AND BEING CONNECTED ACROSS SAID A.C. INPUT, THE OUTPUT CIRCUIT INCLUDING THE OTHER OF (A) SAID THIRD COIL AND (B) THE SERIES COMBINATION OF SAID FIRST AND SECOND COILS AND BEING CONNECTED ACROSS SAID LOAD; SAID INPUT AND OUTPUT ELECTRICAL CIRCUITS FORMING WITH SAID CORE AN INPUT AND AN OUTPUT MAGNETIC CIRCUIT, ONE INCLUDING AT LEAST SUBSTANTIAL PORTIONS OF ALL FOUR OF SAID LEGS AND THE OTHER INCLUDING SAID FIRST AND SECOND LEGS, SAID INPUT AND OUTPUT ELECTRICAL CIRCUITS BEING SO INDUCTIVELY RELATED TO SAID FIRST AND SECOND LEGS THAT THE INPUT AND OUTPUT MAGNETOMOTIVE FORCES GENERATED BY THE INPUT AND OUTPUT CURRENTS AID IN ONE OF SAID FIRST AND SECOND LEG AND OPPOSE IN THE OTHER OF SAID FIRST AND SECOND LEGS; AND A CAPACITIVE REACTANCE, SAID CONTROL ELECTRICAL CIRCUIT INCLUDING SAID CAPACITIVE REACTANCE AND BEING INDUCTIVELY COUPLED TO THE LEG ON WHICH ONE OF SAID FIRST AND SECOND COILS IS WOUND; WHEREBY ALL POWER COUPLED BETWEEN SAID INPUT AND OUTPUT ELECTRICAL CIRCUITS IS IMMEDIATELY COUPLED THROUGH SAID CONTROL ELECTRICAL CIRCUIT, THE CONTROL CURRENT PRODUCING A MAGNETOMOTIVE FORCE IN SAID ONE OF SAID FIRST AND SECOND LEGS IS OF PHASE AND MAGNITUDE TO PRODUCE A RESULTANT OF SAID CONTROL AND OUTPUT MAGNETOMOTIVE FORCES OPPOSITE TO THE OUTPUT MAGNETOMOTIVE FORCE IN SAID LAST-MENTIONED LEG AND THEREBY TO COUPLE POWER FROM THE INPUT TO THE LOAD THROUGH SAID CONTROL ELECTRICAL CIRCUIT AND SAID OUTPUT ELECTRICAL CIRCUIT. 